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Date:      Mon, 20 Jul 1998 12:37:38 -0600
From:      Brett Glass <brett@lariat.org>
To:        Alexandre Snarskii <snar@paranoia.ru>, Alexandre Snarskii <snar@paranoia.ru>
Cc:        security@FreeBSD.ORG
Subject:   Re: The 99,999-bug question: Why can you execute from the stack?
Message-ID:  <199807201837.MAA21687@lariat.lariat.org>
In-Reply-To: <19980720222613.37562@nevalink.ru>
References:  <199807201714.LAA19993@lariat.lariat.org> <199807200148.TAA07794@harmony.village.org> <199807200102.SAA07953@bubba.whistle.com> <199807200148.TAA07794@harmony.village.org> <19980720152932.42290@nevalink.ru> <199807201714.LAA19993@lariat.lariat.org>

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At 10:26 PM 7/20/98 +0400, Alexandre Snarskii wrote:
 
>Can you release kernel patches to realise hardware-level protection ? 
>( I'm not an experienced kernel programer, and have no enough time 
>to learn kernel internals, sorry :( )

The patches would have to be both to the kernel and the compiler, since
the changes would change the machine's segmentation model. I can't
give you an instant evaluation of how extensive they would be; it depends
on how many programs and kernel routines are coded with the assumption 
that the world is totally "flat."

>PS: btw, non-executable stack don't protect against return-into-libc
>attack ( as demonstrated by Rafal Wojtczuk in bugtraq against 
>Solar Designer's patch ).

Segmentation would also guard against another exploit, by the way: jumping
into the middle of a routine to the point just after a security check.
I'm SURE that there are holes like this that haven't been exploited yet.

--Brett


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